The device relates to a safety device that releases abnormally high pressure compressed air outside in a nailing machine that drives a nail with impact by the compressed air.
Generally, a compressed air-driven nailing machine uses compressed air supplied from a compressed air supply source such as a compressor. Since the supply pressure from the compressed air supply source is usually set in accordance with the output of the nailing machine, it is the compressed air at the set pressure that is supplied to the nailing machine. However, compressed air at a high pressure is sometimes mistakenly supplied with confirmation of the initial setting of the supply pressure from the compressed air supply source forgotten. In this case, abnormally high pressure compressed air drives the drive piston, which makes the impact applied to the nail abnormally so large that accidents occur during the nail driving operation. In addition, there is the possibility that the bumper that is subject to the impact of the drive piston will be broken or that the body of the nailing machine will be cracked.
To overcome this problem, a safety device is provided in ordinary nailing machines. The safety device is designed to leak the abnormally high pressure compressed air outside. One known example is disclosed in, e.g., Japanese Unexamined Utility Model Publication No. 50-28779. This safety device is characterized as decreasing the pressure of the compressed air by releasing the compressed air within the nailing machine outside with a compression spring being compressed to open a relief valve when the pressure of the nailing machine exceeds a predetermined value.
However, for the safety device of this type it takes time to decrease the pressure because the device can leak the compressed air only by small amounts per hour. The nail driving operation is likely to start before the pressure has not been completely decreased.
The recent relaxation of the restriction on the usable air pressure has allowed compressed air of quite a high pressure to be employed. This means that a stiffer compression spring should be used. This also means that the strength of the relief valve itself should be increased accordingly, and hence the relief valve must be larger in size. However, since a small-sized nailing machine capable of using high pressure air is called for from the viewpoint of operability, such a design as to increase the size of the relief valve must be avoided.